The art is replete with catalytic converters or oxidation units proposed generally for closed cooking ovens and the like, including for "pyrolytic" self-cleaning, such as in U.S. Pat. Nos. 3,428,435; 3,536,457; and 3,962,561.
In exhausting ovens, in addition to the use of catalytic converters positioned in the oven, it has also been proposed to employ between the product-to-be-cooked and an oxidizing porous catalytic converter layer of layers in the exhaust path, a hot porous metal or ceramic first layer that intercepts the oil fumes and droplet components produced by the cooking and circulated to the exhaust under fan pressure, such first layer seeming to effect the decomposing of such components, as described, for example, in U.S. Pat. No. 4,113,439, while dispersing the oil fumes uniformly over the subsequent catalytic unit.
Such and similar converters have not, however, adequately solved the problems of run-time exhausting and venting of environmentally clean effluents in the different type of apparatus involved in conveyor-operated broilers for so-called "fast food" restaurants and the like. In such apparatus, successive servings of meats and fowl are charbroiled or fried in a continual production line, such as hamburgers, chicken parts and similar food, and in apparatus of the type disclosed, for example, in U.S. Pat. No. 3,646,878 and the like. Such conveyor apparatus has rather demanding environmental emission regulation requirements underlying the required purging and exhausting of the cooking effluent, while also preventing the rapid poisoning of the catalytic converters by components in the cooking effluent. The emissions from, for example, the broiling of fatty hamburgers and the like contain carbon monoxide, organic vapors, aerosols and oily fats, proteins and/or carbohydrates as pollutants for the environs--such constituting all of environmental, health and fire hazards.
In present practice, these problems are somewhat alleviated by diluting the smoke with large amounts of air fan-blown into and through the kitchens and exhausted through hoods and chimneys to the external environment, requiring costly heating and cooling air handling equipment. Such operation, moreover, does not prevent condensation and building up of aerosols in hoods and chimneys, but merely shifts the same amount of air pollutants, including objectionable odors as well, from indoors to the outdoors.
Exhausting chimneys have also been proposed, provided with a small honeycomb ceramic and supplementarily heatable (600.degree. C.) noble metal catalyst to burn the cooking vapors and yield water vapor and carbon dioxide, as described, for example, in U.S. Pat. No. 4,516,486. Catalytic structures of this type are described, also, in U.S. Pat. Nos. 4,102,819 and 4,900,712 of common assignee herewith. A usual feature in the art, indeed, has been the funneling of the cooking smoke from a large fully enclosed cooking area to a small catalyst. The need therefor arose from the sporadic non-uniform smoke release, including practically uncontrollable bursts; and, for example, in broiling, from irregular grease flaming. As pointed out in the before-mentioned U.S. Pat. No. 4,113,439, to the contrary, for efficient operation of the catalytic unit, a uniform flow of volatile (preferably aerosol-free contaminants) is required to attain substantially complete catalytic oxidation effects. Typically, this has required an expensive system involving an enclosed complex cooking apparatus provided with fans and/or heat distributors, or even extra heaters, as above described. Regardless of cost, moreover, such systems are not readily applicable for use with existing open-top broilers or fryers such as are commonly used under hoods in restaurants, additionally inducing undesirable changes in heat distribution which affect adversely the quality of the food, being thus counterproductive.
While the before-mentioned concept of a first hot porous low pressure metal or ceramic screen for intercepting the oil fumes and dispersing the same over the subsequent catalytic unit is indeed useful with such charbroiler or similar conveyor-line broilers with which the present invention is largely concerned, such cannot of itself protect the subsequently positioned catalysts from being poisoned by finely divided solid inorganics, including particularly salt (e.g. sodium chloride and potassium chloride) and oxides of phosphorous resulting from the decomposition of phospholipids and entrained in the smoke and deposited, at least in substantial part, upon the catalyst.
It is to the solution of this and related problems particularly of concern with conveyer-line and similar charbroiler type apparatus and the like that the improvement of the present invention is primarily concerned, it having now been discovered that if such initial dispersing screen is not just of metal or ceramic, but is appropriately coated and also dimensioned to overlie substantially the complete broiling area (say from about three-quarters to one and a quarter the broiling area), such can admirably simultaneously serve markedly to adsorb and entrap such deleterious inorganics without at all impairing its oil fume and flame interception, arresting and dispersing functions, and can thus greatly reduce catalyst poisoning, increasing the catalyst life.